Analysis of Geosmin and 2-Methylisoborneol Utilizing the Stratum PTC and Aquatek 70

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1 Analysis of Geosmin and 2-Methylisoborneol Utilizing the Stratum PTC and Aquatek 70 Application Note Abstract Geosmin and 2-Methylisoborneol are organic compounds that have a distinct scent. These compounds also have an extremely low odor detection threshold and because of this, many drinking water laboratories require detection levels of below 10ppt. This application note investigates the detection of Geosmin and 2-Methylisoborneol at a one part per trillion level utilizing Purge and Trap (P&T) coupled with a Gas Chromatograph and Mass Spectrometer (GC/MS). Introduction Geosmin and 2-Methylisoborneol have very poor purge efficiencies. In order to detect these compounds down to the 1ppt level it was necessary to optimize the P&T and GC/MS techniques. In this study, the GC/MS was run in Selective Ion Monitoring (SIM) mode while the P&T conditions were modified in order to achieve a 1ppt level of detection. A 10% (w/v) salt solution was utilized along with a 25mL purge volume in order to aid in compound detection. The Stratum PTC was configured with a #1 trap and three different injection techniques were examined in order to determine the optimum method for injection. Experimental-Instrument Conditions The Stratum PTC and Aquatek 70 Autosampler were coupled to an Agilent 7890A GC and a 5975 inert XL MS system for analysis. A #1 trap was the analytical trap used. The GC was configured with a J&W Scientific DB-VRX 30m x 0.250mm x 1.4μm column. The MS scanned in the SIM mode. The Stratum PTC transfer line was configured to the GC column three different ways. The first was through a cryofocusing module, the second was through the Split/Splitless inlet of the GC and the third configuration was a direct column connection. Finally, a 25mL purge volume of 10% (w/v) salt water was used. The GC/MS parameters are outlined in Tables 1 and 2 respectively while Tables 3 and 4 outline the P&T conditions. GC Parameters MSD Parameters GC: Agilent 7890A MSD: Agilent 5975C inert XL Column: J&W Scientific DB-VRX 30m x 0.250mm x1.4um Source: 230 C Oven Program: 40 C for 2.0 min; 16 C/min to 160 C for 0 min; 20 C /min to 240 C for 5.0 min; 18.5 min. runtime Quad: 150 C Inlet: 220 C Solvent Delay: 5.0 min Column Flow: 1.02mL/min SIM Ions 95, 107, 108, 112, 125, 126 Split: (Used for Split/Splitless 10:1 Dwell Time: 100 msec dwell per ion Inlet Injection only) Gas: Helium Pressure: psig Table 1: GC Parameters Table 2: MS Parameters Sales/Support: Main:

2 Stratum PTC and AQUATek 70 Parameters Water Parameters for Cryofocusing Injection Variable Value Variable Value Pressurize Time 0.60 min Purge Time Fill IS Time 0.00 min Purge Temp 0 C Sample Transfer Time 0.75 min Purge Flow 45mL/min Rinse Loop Time 0.75 min Dry Purge Time 5.00 min Purge Loop Time 1.00 min Dry Purge Temp 20 C Bake Rinse On Dry Purge Flow 45mL/min Number of Bake Rinses 3 GC Start End of Desorb Bake Drain Time 1.50 min Desorb Preheat Temp 220 C Bake Drain Flow 250mL/min Desorb Drain On Valve Oven Temp 175 C Desorb Time 6.00 min Transfer Line Temp 175 C Desorb Temp 225 C Sample Mount Temp 60 C Desorb Flow 300mL/min Purge ready Temp 40 C Bake Time min Condenser Ready Temp 40 C Bake Temp 230 C Condenser Purge Temp 20 C Bake Flow 250mL/min Standby Flow 45mL/min Condenser Bake Temp 175 C Pre-Purge Time 0.0 min Focus Temp -100 C Pre-Purge Flow 0.0mL/min Inject Time 2.00 min Sample Heater On Inject Temp 200 C Sample Preheat Time 0.01 min Standby Temp 150 C Sample Temp 40 C Table 3: Stratum PTC and AQUATek Parameters for a Cryofocusing Injection Stratum PTC Parameters are in Blue Cryofocusing Parameters are in Green Stratum PTC and AQUATek 70 Parameters Water Parameters for Split/Splitless Inlet and Direct Column Injections Variable Value Variable Value Pressurize Time 0.60 min Purge Time Fill IS Time 0.00 min Purge Temp 0 C Sample Transfer Time 0.75 min Purge Flow 100mL/min Rinse Loop Time 0.75 min Dry Purge Time 5.00 min Purge Loop Time 1.00 min Dry Purge Temp 20 C Bake Rinse On Dry Purge Flow 45mL/min Number of Bake Rinses 3 GC Start Start of Desorb Bake Drain Time 1.50 min Desorb Preheat Temp 220 C Bake Drain Flow 250mL/min Desorb Drain On

3 Valve Oven Temp 175 C Desorb Time 2.00 min Transfer Line Temp 175 C Desorb Temp 225 C Sample Mount Temp 60 C Desorb Flow 300mL/min Purge ready Temp 40 C Bake Time min Condenser Ready Temp 40 C Bake Temp 230 C Condenser Purge Temp 20 C Bake Flow 250mL/min Standby Flow 45mL/min Condenser Bake Temp 175 C Pre-Purge Time Pre-Purge Flow Sample Heater Sample Preheat Time 0.0 min 0.0mL/min On 0.01 min Sample Temp 40 C Table 4: Stratum PTC and Aquatek Parameters for Split/Splitless Inlet and Direct Column Injections Stratum PTC Parameters are in Blue A 50ppb working calibration standard was prepared in methanol. standards were prepared in a 50mL volumetric flask and filled to volume with 10% (w/v) de-ionized salt water solution. The calibration range was ppt. The standards were transferred to headspace free 40mL vials for analysis. The calibration data was analyzed using Agilent Chemstation software. The calculated linear regression and the of each compound and their respective injection techniques are outlined in Tables 5, 6 and 7. Method Detection Limit (), Carryover, and and Accuracy Study A statistical determination of the s was determined for both of the compounds with each injection technique by analyzing seven replicate standards of a 1ppt calibration standard. Furthermore, seven replicate standards of a 10ppt calibration standard were analyzed for each injection method in order to determine the precision and accuracy of the experimental conditions. Finally, three blanks were run after a high, 100ppt calibration standard in order to determine percent carryover for each technique. The detection limits, precision and accuracy data and percent carryover for each compound and their respective injection method are provided in Tables 5, 6, and 7. Compound % Carryover Geosmin Methylisoborneol Table 5: Cryofucusing Injection Experimental Results Summary Compound %Carryover Geosmin Methylisoborneol Table 6: Split/Splitless Inlet Injection Experimental Results Summary

4 Compound %Carryover Geosmin Methylisoborneol Table 7: Direct Column Injection Experimental Results Summary Figure 1: Total Ion Chromatogram of a 50ppt Geosmin and 2-Methylisoborneol Standard Using Cryofocusing Injection Figure 2: Total Ion Chromatogram of a 50ppt Geosmin and 2-Methylisoborneol Standard using Split/Splitless Inlet Injection

5 Figure 3: Total Ion Chromatogram of a 50ppt Geosmin and 2-Methylisoborneol Standard Using a Direct Column Injection Conclusions The Stratum PTC and AQUATek 70 configured with an Agilent GC/MS system operating in SIM mode performed very well in detecting Geosmin and 2-Methylisoborneol with all three injection techniques. The linearity of all of the curves was for both compounds with a of below 10%. The system displayed excellent accuracy and precision results and the detection limits for the compounds were below 0.250ppt for all three injection methods. The 25mL sample volume and 10% (w/v) salt solution aided in increasing the purge efficiency of both the Geosmin and the 2-Methylisoborneol compounds. Further analysis of the compound responses for all three techniques displayed that the direct column injection configuration had the optimum compound response, thus although the three techniques all showed consistent analytical results and comparable detection limits, I would recommend the direct column injection for Geosmin and 2-Methylisoborneol detection down to a 1ppt level.